Still now, although there are many kinds of dimmers have been developed already. Two major kinds of dimmers are still commonly used. The first kind is an electronic ballast that is depicted in FIG. 1. Please refer to FIG. 1, which is a schematic diagram showing a circuit of a dimming control system according to a traditional electronic ballast. The traditional electronic ballast 11 uses a four-wire frequency-modulated dimming system. A variable resistor 13 is used in the electronic ballast 11 for controlling the operating frequency of the electronic ballast 11. The AC line voltage Vac applied to a discharge lamp 12 regulates the light intensity of the discharge lamp 12 through frequency-modulated control. The advantage of traditional electronic ballast 11 is that the discharge lamp does not suffer heavy damages after operating a pretty long time under the condition of a low power level. If the damages are happened to the lighting equipments, the construction cost will be pretty expensive.
The second traditional dimmer is a phase-controlled dimmer. A phase control of the AC line voltage is used to drive a lighting equipment for regulating the brightness of the lighting equipment. Please refer to FIG. 2, which is a schematic diagram showing a circuit of a dimming control system according to a traditional phase-controlled dimmer. The TRIAC dimmer 20 seriously connected with a tungsten lamp 21 uses a thyristor to be supplied a positive gate pulse of a short duration at the appointed phase angle of every half circle of the AC line voltage, and then the AC line voltage supplies the output power to the tungsten lamp 21. The phase-controlled dimmer of the prior art is in some range of light intensity form 0% to 100% of output power, for example. The disadvantage of the tungsten lamp 21 is not suitable for the dimming control of electronic ballast.
From the above description, it is known that how to design a dimming control system for providing an efficient and convenient dimming control has become a major problem waited to be solved. In order to overcome the drawbacks in the prior art, a frequency-modulated dimming control system of a discharge lamp is provided. The particular design in the present invention not only solves the problem described above, but also uses a simple circuit to accurately regulate the light intensity of a discharge lamp. It does not need to alter the setting of a power cord and can provide a wide dimming range. Thus, the invention has the utility for the industry.
Therefore, the present invention provides a frequency-modulated dimming control system of a discharge lamp which overcomes the disadvantages described above.